Sea stars have no brain and no blood.

Sea stars belong to a group of animals called echinoderms. They do not have a central brain to make decisions. Instead, they have a ring of nerves around their mouth and nerves that run down each arm. This allows each arm to sense light, touch, and chemicals in the water independently.Instead of a heart and blood, sea stars use a water vascular system. Seawater enters through a small, hard spot on their top side called a madreporite. The animal pumps this water through canals to reach hundreds of tiny tube feet. By changing the water pressure, the sea star can stretch or shrink these feet to walk.This hydraulic pressure is strong enough to pull apart the shells of clams and mussels. Because they use seawater, they do not need a heart or red blood cells to carry oxygen. This decentralized body plan also helps them survive injuries. If a sea star loses an arm, it can often grow a new one back. Some species can even grow a whole new body from just one arm and a piece of their center.